keep octopus before, they will escape through any hole.
Had one for well over a year before he managed to pry open the lid and ended up dead on the carpet across the room. They will completely relandscape your tank, nothing will be safe.
in saying that, they are great pets, intelligent and curious. Mine use to come to the top of the tank when people entered the room and squirt water at them through a small hole, a good solid jet from an octi would go 2-3 m acoss the room and drench unsuspecting visiters :lol:
Crabs are great food, throw some big crabs in and watch him dismantle them.